A known industrial process for the conversion of hydrogen sulphide is the so-called Claus process. In a Claus process hydrogen sulphide is reacted with sulphur dioxide to elemental sulphur and water according to the Claus reaction.2H2S+SO22H2O+3/nSn  (1)
Conventionally, this reaction is performed in several stages at temperatures in the rage of from 200 to 240° C. and at near atmospheric pressures.
In U.S. Pat. No. 4,280,990 is disclosed a process for removing hydrogen sulphide from a natural or industrial gas using a modified Claus process for reacting hydrogen sulphide with sulphur dioxide at temperatures of at least 160° C. and at elevated pressures in the presence of liquid sulphur. This is supported by Shields et al., Ind. Eng. Chem. Res., 2007, 46, p7721 to 7728, where it is shown for lean gas mixtures 0.95% hydrogen sulphide and 0.50% sulphur dioxide in nitrogen some hydrogen sulphide conversion (22.5%) could be obtained in the absence of hydrocarbons at a temperature of 135° C. and 296 kPa pressure.
Hydrogen sulphide is typically obtained as part of a larger volume of hydrocarbon feed gas, typically a hydrocarbon feed gas, such a natural gas. In all conventional Claus processes, including the process disclosed in U.S. Pat. No. 4,280,990, hydrogen sulphide is first separated from a hydrocarbon gas stream, e.g. by a solvent extraction process. After solvent regeneration, a hydrogen sulphide-rich gas is obtained which is dealt with in the Claus process. About one third of the hydrogen sulphide in this gas is oxidized with air to sulphur dioxide in a burner, according to:2H2S+3O22H2O+2SO2  (2)
The sulphur dioxide subsequently reacts with the remaining hydrogen sulphide to elemental sulphur according to reaction (1).
The hydrogen sulphide has first to be separated from the remainder of the gas to prevent combustion of the hydrocarbons (or hydrogen) in the feed gas. It would be advantageous if hydrogen sulphide could be selectively oxidized, i.e. without the need to separate it from the remainder of the gas.
Shields et al., Ind. Eng. Chem. Res., 2007, 46, p7721 to 7728, disclose that hydrogen sulphide may be directly selectively oxidised using molecular-oxygen as oxidant in the presence of a catalyst and liquid sulphur. However, this has the disadvantage that the liquid sulphur is oxidised to sulphur dioxide due to reaction with the molecular-oxygen.
In P. D. Clark, Controlling CO2 emissions in large scale sour gas developments, Alberta Sulphur Research Limited, Quarterly Bulletin of ASRL, June 2008, page 45 to 55, a high pressure Claus process is disclosed wherein a sour natural gas stream is processed to remove hydrogen sulphide. In this process one third of sour gas is combusted with pure oxygen to provide a gas comprising sulphur dioxide and water, the remaining two thirds of the sour gas are passed through a carbon bed to remove mercaptans and any other contaminants. Subsequently, the sulphur dioxide and water-comprising gas and the mercaptan-depleted sour gas are provided to a reactor and allowed to react over an alumina catalyst. It is suggested to use a hydrogen sulphide to sulphur dioxide ratio of more than 2 resulting in an effluent of the reactor comprising liquid sulphur, methane, carbon dioxide hydrogen sulphide and water.
There is a need in the art for a process for the direct selective oxidation of hydrogen sulphide, that is suitable for the deep desulphurisation of gaseous hydrocarbon or hydrogen-comprising streams with a relatively high hydrogen sulphide content, i.e. above 0.5 vol % and up to 25-50 vol %, which does not require the separation of hydrogen sulphide or mercaptans from the hydrocarbon-comprising feed nor requires to combust significant parts of the hydrocarbons in the hydrocarbon-comprising feed and wherein the oxidation of the liquid sulphur by the oxidant is prevented.